Corundum Value, Price, and Jewelry Information

The corundum family of gemstones consists of ruby and sapphire. Corundum is very compact, dense, and lacks gemstone cleavage. It's also the second hardest natural mineral after diamond. Gem-quality corundum is also quite rare. These factors make both varieties of corundum some of the most highly desired jewelry stones. Ruby is the red variety of corundum. All other colors of corundum, including colorless, are called sapphires.

Corundum Value

Rubies and sapphires are some of the most valuable and popular of all gemstones. Despite the enormous size of these stones in museums and royal collections, most corundum gems available for sale are usually of more modest size. A 3-4 carat ruby of fine quality would be a rare and very expensive gem in today's market. Sapphires over 5 carats, clean and with good blue color, are similarly rare and also valuable. Relatively speaking, there is an abundance of good quality small sapphires but not rubies. Very few known ruby deposits can be actively worked, while there are many more sapphire deposits being actively mined.

Burma Rubies

Certified origin. Untreated material.
Average brilliancy of 30 to 40%. Add up to 20% or deduct to 10% for other cutting.
Prices for ovals and cushions. Add 7% to 10% for rounds, pears, marquis. Add 15% to30% for emerald cuts.
Top Color: R 6/6
No trade data available. As of May 2015, the record price for a ruby is approximately 2 million per carat. ( million for a 25.59 carat Mogok "pigeon's blood" ruby).
Very Good Color: R 5/6, 7/5; slpR 5/6, 6/6, 7/5; stpR 6/6.

Very Good Color

.5 to .75 carat

.75 to 1 carat

1 to 2 carats

2 carats plus

VVS

to /ct

to ,500/ct

,000 to ,000/ct

to ,000/ct

VS/SI

to /ct

to ,600/ct

,000 to ,500/ct

to ,000/ct

SI/I

to /ct

to /ct

to ,000/ct

to ,000/ct

Good Color: R 6/5; slpR 6/5; stpR 5/6

Good Color

.5 to .75 carat

.75 to 1 carat

1 to 2 carats

2 carats plus

VVS

to /ct

to /ct

to ,000/ct

to ,000/ct

VS/SI

to /ct

to /ct

to ,800/ct

to ,000/ct

SI/I

to /ct

to /ct

to ,700/ct

to ,000/ct

Fair Color: R 5/5, 6/4, 7/4; slpR 5/5, 6/4, 7/4.

Fair Color

.5 to .75 carat

.75 to 1 carat

1 to 2 carats

2 carats plus

VVS

to /ct

to /ct

to /ct

to ,000/ct

VS/SI

to /ct

to /ct

to /ct

to ,000/ct

SI/I

to /ct

to /ct

to /ct

to ,000/ct

Other Rubies

Heat treated material.
Average brilliancy of 40 to 60%. Add up to 20% or deduct to 10% for other cutting.
Prices for ovals and cushions. Add 7% to 10% for rounds, pears, marquis. Add 15% to 30% for emerald cuts.
Top Color: R 6/6
No trade data available.
Very Good Color: R 5/6, 7/5; slpR 5/6, 6/6, 7/5; stpR 6/6.

Kashmir Sapphire

Certified origin. Untreated material.
Average brilliancy of 40 to 60%. Add to 20% or deduct to 10% for other cutting.
Prices for ovals and cushions. Add 8% to 10% for rounds and pears. Add 10% to 20% for emeralds and marquis.
Top Grade: vB 5/6, 6/6. B 5/6, 6/6.

Other Blue Sapphires

Heat treated material. Average brilliancy of 40% to 60%. Add to 20% or deduct to 10% for other cutting.
Prices for ovals and cushions. Add 8% to 10% for rounds and pears. Add 10% to 20% for emeralds and marquis.
Note: If certified Burmese and untreated, add 50%, except fair or lower grades.
Top Grade: vB 5/6, 6/6; B 5/6, 6/6.

Metamorphosed crystalline limestones and dolomites, as well as other metamorphic rock types such as gneiss and schist. Also, igneous rocks such as granite and nepheline syenite. Gem-quality corundum is often found in placer deposits. Non-gem corundum is abundant throughout the world.

Inclusions

Star corundum gemstones show asterism, or a “star effect.” This phenomenon is created by the inclusion of rutile needles within the host corundum crystal. The rutile needles orient themselves according to the hexagonal symmetry of the corundum, and reflections from these needles provide a chatoyancy. When such material is cut into a cabochon the sheen is concentrated along the top of the stone into three white lines crossing at 120° angles, creating a six-rayed star. Very rarely there are two distinct sets of needles oriented according to the first and second order prisms of the corundum (30° apart), resulting in a strong, 12-rayed star.

Enhancements

Heat treatment: improves clarity and sometimes color, also used to improve asterism in ruby. Common, often undetectable. Detect with magnification, (halos around included crystals.) Also, if inert and no absorption lines, stone is probably heat treated.

Diffusion: improves color or asterism, occasional to common for blue sapphire and star ruby, rare for other colors, stable, detect with immersion and magnification.

Stone Sizes

Sapphires, in general, reach a far greater size than rubies. A ruby of 30 carats is a great rarity, whereas sapphires in museum collections weighing hundreds of carats are not uncommon. The largest rubies come from the chrome-zoisite matrix in Tanzania, but these are not really of gem quality. Fine gem rubies of large size occur in the Sri Lankan gravels, with smaller ones from Burma and Thailand. Enormous sapphires of fine color and transparency have been found in the gem gravels of Sri Lanka and Burma. (Most are from Sri Lanka). A 1400 gram ruby was found in Yugoslavia (Prilip) but was not gemmy. Malawi material (sapphire) reaches a size of about 12 carats. Large sapphires have been found in Australia. Montana sapphires over 1 carat are very rare, but the blue ones in this size range are magnificent.

Specific gemstones of significant size are described in the ruby and sapphire entries.